Stepping toward the carbon circular economy (CCE): Integration of solar chemistry and biosystems for an effective CO2 conversion into added value chemicals and fuels

The substitution of fossil-C is an urgent task for both the scarcity of resources and stopping the emission of green-house gases, (GHGs) that impact the climate of our planet. The transfer to the atmosphere of heat, due to the inefficiency of conversion of chemical energy into other forms of energy, and CO2 is also causing the increase of atmospheric water vapor, a stronger and more abundant greenhouse gas than CO2: all actors (heat, CO2 and H2Ov) concur to increase the temperature of the planet. Partial substitution of fossil-C can be achieved by using biomass, but that alone cannot produce all the energy and goods necessary for our society. Carbon will still be present in our future, but the solution to our problems is integrating solar chemistry and biotechnologies for using atmospheric CO2. This chapter, after an introduction to Carbon Circular Economy-CCE and CO2 utilization in Chemical Industry, considers the various options available of using solar energy for CO2 conversion into energy vectors that may allow to continue to use the existing infrastructures in transport and every-day life. Two options are considered: (i) solar-based water splitting and use of H2 for chemo-catalytic CO2 conversion using known processes, or (ii) photo-co-processing of water and CO2 to afford energy products and chemicals without H2 generation, a most innovative technology. The state of the art is provided and barriers to overcome for a large-scale exploitation of the two options are highlighted. The contribution to fossil-C substitution that may come from integration of solar chemistry with material science and biotechnology concludes this chapter.